1. Field of the Invention
The present invention relates to a member mount elastically connecting a suspension member and a vehicle body of an automobile and isolating vibration therebetween, and an assembly structure of the member mount.
2. Description of Related Art
A suspension member, such as a sub-frame, is a skeletal frame member of a part of a vehicle to mount a suspension. The suspension is assembled to a vehicle body through the suspension member. In general, the suspension member and the vehicle body are elastically connected by a member mount. The member mount maintains a proper relative positional relationship between the suspension member and the vehicle body, isolates vibration of a suspension system transmitted to the vehicle body through the suspension member, and conversely, transmits a driving force and a braking force to the vehicle body. In case of a sub- frame, an engine and a transmission are mounted in addition to the suspension. In this case, the member mount, which elastically connects the sub-frame and the vehicle body, also isolates vibration from the engine.
As disclosed in Related Art 1, a member mount of this type generally has a rigid inner tubular member, a rigid outer tubular member surrounding the inner tubular member in a position radially away therefrom, and a rubber elastic body radially connecting the inner tubular member and the outer tubular member. The outer tubular member is fixed to a suspension member and the inner tubular member is fixed to a vehicle body, and thereby the suspension member and the vehicle body are elastically connected and vibration is isolated.
FIG. 7 is an example of a conventionally known member mount. The drawing illustrates a vehicle body member 200, a sub-frame (octothorpe (hash-character)-shaped sub-frame) 202 as a suspension member, a member mount 204, and an upper stopper 206. The member mount 204 has a rigid inner tubular member 208 composed of a tubular-shaped metal, a rigid outer tubular member 210 composed of a tubular-shaped metal and surrounding the inner tubular member 208 in a position radially away therefrom, and a tubular rubber elastic body 212 integrally vulcanized and attached in a state of radially connecting the inner tubular member 208 and the outer tubular member 210.
The member mount 204 is press-fitted and fixed to the sub-frame 202 in the outer tubular member 210 and is fixed to the vehicle body member 200 through a fastening bolt 218 in the inner tubular member 208. Specifically, an inner hole 214 is provided inside the inner tubular member 208. A positioning nut 216 is inserted from the vehicle body member 200 into the inner hole 214 in a downward direction in the drawing, the positioning nut 216 having a tubular portion and serving as a positioning member. The fastening bolt 218, which is inserted into the inner tubular member 208 from below in an upward direction in the drawing, is screwed into a female thread hole 220 in a central portion of the positioning nut 216. Thereby, the inner tubular member 208 is fastened and fixed to the vehicle body member 200 with the fastening bolt 218 and the positioning nut 216.
A projection 222 projecting externally in the radial direction along the entire periphery is provided on an outer peripheral surface of the inner tubular member 208. The inner tubular member 208 partially has a thick portion 224 projecting externally in the axial direction in the portion of the projection 222. The projection 222 is provided to harden a spring in a direction perpendicular to the axis of the rubber elastic body 212 and to enhance running stability of a vehicle. The entirety of the projection 222 is internally embedded in the rubber elastic body 212.
The positioning nut 216 positions the member mount 204, specifically its inner tubular member 208, relative to the vehicle body member 200. The positioning nut 216 has a tubular portion 217 having a circular external periphery and is fixed to the vehicle body member 200 by welding in advance.
A forged article is conventionally used as the inner tubular member 208 of the member mount 204. The internal peripheral surface of the inner tubular member 208, specifically the inner hole 214, and the outer peripheral surface are shaped concurrently at the time of forging the inner tubular member 208.
With the member mount 204, however, the metal inner tubular member 208 formed of a forged article is inevitably heavy. Furthermore, the processing cost is high due to individual forging and forming of the inner tubular member 208, increasing the cost of the member mount 204. Improvements are thus desired.
In order to connect the sub-frame 202 to the vehicle body member 200 through the member mount 204, the member mount 204 is fixed to the sub-frame 202 in advance. In this state, the member mount 204, specifically the inner tubular member 208, is fixed to the vehicle body member 200, and thereby the sub-frame 202 and the vehicle body member 200 are connected. At this time, the sub-frame 202 should be connected so as to have a predetermined proper relative positional relationship with the vehicle body member 200.
In the case where inner holes 214 of all inner tubular members 208 of four member mounts 204 disposed at four corner portions of the sub-frame 202, as shown in FIG. 8, have the same inner diameters to be fitted to four corresponding positioning nuts 216 in the vehicle body member 200 with no gap around the entire periphery, the member mounts 204 cannot practically be assembled to the vehicle body member 200 such that the positioning nuts 216 are inserted into the inner tubular members 208 in a state where the four member mounts 204 are mounted on the sub-frame 202 in advance. This is because a positional error generally occurs between the axis center of each of the four positioning nuts 216 and the axis center of each of the inner tubular members 208 of the four corresponding member mounts 204.
Conventionally, in any of the four member mounts 204, for example, the member mount 204 at a position P1 in FIG. 8, the inner hole of the inner tubular member 208 is provided as a circular inner hole 214A, which is properly fitted to the positioning nut 216 along the entire periphery and is defined as a reference hole. In the member mount 204 at a position P2 different from the position P1, the inner hole of the inner tubular member 208 is provided as an inner hole 2148, which is an elongated hole having a short diameter properly fitted to the positioning nut 216 and a long diameter greater than the short diameter and having a looseness relative to the positioning nut 216 and is defined as a sub-reference hole. In the member mounts 204 in positions P3 and P4 different from the positions P1 and P2, the inner holes of the inner tubular members 208 are provided as inner holes 214C, each having a large diameter having a looseness along the entire periphery relative to the positioning nut 216. The positioning nut 216 is fitted to the circular hole 214A as the reference hole, and thereby the sub-frame 202 is positioned at the position P1 in two orthogonal directions in the direction perpendicular to the axis of the vehicle body member 200. The positioning nut 216 is fitted to the short diameter of the elongated inner hole 214B, and thereby the sub-frame 202 is positioned in one direction perpendicular to the axis (left-right direction in FIG. 8). At this time, a looseness occurs between the positioning nut 216 and the inner hole 214B in the other direction perpendicular to the axis of the elongated inner hole 214B (vertical direction in FIG. 8), thus absorbing a displacement of the each of the axis centers of the positioning nut 216 and the inner hole 214B.
The member mounts 204 at the other positions P3 and P4 each have the inner hole 214C having a larger diameter than the positioning nut 216 and having a looseness along the entire periphery relative to the positioning nut 216. The looseness absorbs a positional error in the two orthogonal directions in the direction perpendicular to the axis in each of the inner holes 214C of the positions P3 and P4. Thereby, the sub-frame 202 can be assembled to the vehicle body member 200 in a proper relative positional relationship. The member mounts 204 at the positions P1 and P2 in FIG. 8 are same in the configuration other than the shape of the inner hole. The member mounts 204 at the positions P3 and P4 are different in the configuration and properties from the member mounts 204 at the positions P1 and P2.
In this case, however, the inner tubular members 208 should have the inner holes 214 different in the shape, though the member mounts 204 at the positions P1 and P2 are same. In other words, separate forged articles should be prepared for the inner tubular members 208. Preparing the inner tubular members 208 formed of two types of forged articles requires separate production (forging) processes, thus leading to an increase in the cost required for the inner tubular members 208.
A proposal of the inventor of the present invention is that a tubular metal pipe material having an inner diameter greater than the outer diameter of the positioning nut 216 is used as the inner tubular member 208. An inner peripheral resin layer having a tubular shape is layered on an inner peripheral surface thereof, and an outer peripheral resin layer having a tubular shape is provided on an outer peripheral surface thereof. The resin layers are connected in a resin connection portion in a connection hole passing through the internal tubular member 208. The inner hole 214 is thus provided by the inner peripheral resin layer, into which a positioning member, such as the positioning nut 216, is inserted.
An example of such a configuration is shown in FIGS. 9A and 9B. The drawing illustrates an inner tubular member 208 composed of a metal pipe material, an inner peripheral resin layer 226 layered on an inner peripheral surface thereof, an outer peripheral resin layer 228 layered on an outer peripheral surface of the inner tubular member 208, a connection hole 230 provided in the inner tubular member 208, and a resin connection portion 232 in the connection hole 230. The inner peripheral resin layer 226 and the outer peripheral resin layer 228 are connected to each other inside and outside in the resin connection portion 232.
The inner peripheral resin layer 226 and the outer peripheral resin layer 228 are not adhered to the inner tubular member 208 composed of a metal pipe material. The inner peripheral resin layer 226 and the outer peripheral resin layer 228 are held to the inner tubular member 208 through connection in the resin connection portion 232. Two connection holes 230 and resin connection portions 232 are provided in positions 180° away in the circumferential direction and opposite to each other in the direction perpendicular to the axis.
In this configuration in which the inner peripheral resin layer 226 is layered on the inner peripheral surface of the rigid metal inner tubular member 208 and the inner hole 214 is provided by the inner peripheral resin layer 226, the inner hole 214A at the position P1 as the reference hole and the inner hole 214B at the position P2 as the sub-reference hole in FIG. 8 can be readily provided inside the respective inner tubular members 208 by changing the shape of the inner peripheral resin layer 226 using the same rigid metal inner tubular member 208.
In test production of a composite member of the metal inner tubular member 208, the inner peripheral resin layer 226, and the outer peripheral resin layer 228, the composite member having the circular inner hole 214, however, it turns out that the inner peripheral resin layer 226 peels off from the inner peripheral surface of the inner tubular member 208 and that the shape turns to be an ellipse, as shown in FIG. 9B.
The ellipse phenomenon occurs because, as shown in FIG. 9B, the inner peripheral resin layer 226 shrinks due to cooling after molding; the portion other than the portion bound by the resin connection portion 232 peels off from the inner peripheral surface of the inner tubular member 208, thus deforming in the reduced-diameter direction; and accordingly, the entire shape of the inner peripheral resin layer 226 changes to an ellipse.
The ellipse-shaped inner peripheral resin layer 226, specifically the ellipse-shaped inner hole 214, prevents the positioning nut 216 as a positioning member from being inserted through the inner hole 214. Thus, the member mount 204, specifically the sub-frame 202, cannot be assembled to the vehicle body member 200. In FIG. 9B, the long hole diameter after the shape changes to an ellipse is represented by “a,” and the short hole diameter by “b.”
The example above is a case where the circular inner hole 214 is provided in the inner peripheral resin layer 226. A similar circumstance also arises in a case where the elongated inner hole 214 is provided in the inner peripheral resin layer 226. Specifically, deformation of the inner peripheral resin layer 226 in the reduced-diameter direction in the short diameter prevents the positioning nut 216 from being inserted therethrough. Deformation in the reduced-diameter direction in the long diameter reduces a looseness relative to the positioning nut 216, thus preventing the original purpose from being attained.
As related art of the present invention, Related Art 2 discloses a member mount in which an inner peripheral resin layer is provided on an inner peripheral surface of a metal inner tubular member; an outer peripheral resin layer is provided on an outer peripheral surface thereof; and a resin connection portion connects the resin layers through the inner tubular member. The disclosure of Related Art 2, however, is intended to pre-compress a rubber elastic member from the inner periphery and does not recite the purpose and method of resolution of the present invention, thus being different from the present invention.
[Related Art 1] Japanese Patent Laid-open Publication No. H7-4457
[Related Art 2] Japanese Patent Laid-open Publication No. 2007-263148